I'm looking for BIOS: Asus Radeon HD 7970 DirectCU II TOP, for second switch position(DVI-Dual Link). I want to start 120Hz on 1080p on my gaming monitor.
My first BIOS version is 6798.15.12.0.4.AS05.U3.

And the problem is this:
I flashed second BIOS, but something went wrong. When I start computer on the second BIOS, nothing happens. Black screen. What's the problem? What I can do?
How can I do something when see black screen?

Use position 1 to boot into ATiFlash, when you are actually ready to flash the new bios on to your card, switch it to position 2 and flash it. Check the VGA bios collection for the bios you need: http://www.techpowerup.com/vgabios/

I see. I have 6798.15.12.0.4.AS05.U3, and it's Single Link. Maybe U2 is Dual Link.
So I can flash this U2? (6798.15.12.0.4.AS09.U2)

Click to expand...

Potentially, yes, but as I mentioned earlier, some BIOSes don't work on all cards, so flash may result in no boot.

Which is no big deal, since you have other BIOS to recover from.

Also, many users say that 2560x1600 doesn't work with this card. I had not tested. So maybe use DP port working or not to check if U3 or U2 is "dual-link". That's how it works, it disables DP ports to make dual-link DVI.